1. Field of the Invention
This invention relates to a low noise level automotive internal combustion engine, and more particularly to an engine equipped with a bearing beam structure for supporting a crankshaft in a manner to improve the mechanical strength of a cylinder block.
2. Description of the Prior Art
In connection with engine noise, noise emitted from a cylinder block skirt section or oil pan is mainly caused by vibration of the cylinder block itself. In order to reduce vibration induced noise, it seems enough to suppress the vibration, due to explosion torque which is applied to a crankshaft, by increasing the rigidity of the cylinder block. However, this unavoidably leads to an increase in cylinder block wall thickness and accordingly to a considerable increase in engine weight, thereby giving rise to new problems such as increased fuel consumption. In view of this, a variety of approaches have been made to improve the rigidity of the cylinder block while minimizing any increase in cylinder block weight. In connection with one of these approaches, attention has been paid to the employment of a bearing beam structure which securely connects a plurality of bearing caps for supporting the crankshaft, in order to improve the mechanical strength of bearing caps and engine parts associated with them.